R700 not connecting with 256 QAM speeds (MCS 8, 9)

unknown

My standalone R700 will not use MCS 8 or 9 for any clients connected over the 5GHz 80Mhz AC-band. Even when the client is very close to the AP with direct line of sight, the MCS index stays at 7 with a reported Tx rate of  878Mbps. How can I get it to use the higher and faster 256 QAM rates of MCS 8 and 9? The clients, for example Macbook Pros, do support 256 QAM, so that should not be the issue.

Specs:
R700
Firmware 100.1.0.0.432

Macbookpro
OS X El Capitan 10.11.6

Interfaces:

en0:

  Card Type: AirPort Extreme  (0x14E4, 0x133)

  Firmware Version: Broadcom BCM43xx 1.0 (7.21.95.175.1a6)

  MAC Address: f4:5c:89:c2:86:25

  Locale: FCC

  Country Code: US

  Supported PHY Modes: 802.11 a/b/g/n/ac

  Supported Channels: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 36, 40, 44, 48, 52, 56, 60, 64, 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140, 144, 149, 153, 157, 161, 165

  Wake On Wireless: Supported

  AirDrop: Supported, Channel 149

  Status: Connected

  Current Network Information:

K-Town R 5G:

  PHY Mode: 802.11ac

  BSSID: 2c:c5:d3:24:3f:0c

  Channel: 149

  Country Code: US

  Network Type: Infrastructure

  Security: WPA2 Personal

  Signal / Noise: -38 dBm / -92 dBm

  Transmit Rate: 878

  MCS Index: 7

john_d

So the diagnostics you're looking at on your Mac is showing the Tx rate from the perspective of the client. That is, client -> AP "upload". This transmit rate is 100% under the control of the client, and the client is choosing it.

In the other direction, the Ruckus AP will choose the best transmit speed, the one that leads to the highest observed throughput. This is not necessarily the highest MCS rate. And thousands of packets are sent per second, while what you are looking at is a very instantaneous snapshot of the last-used Tx rate.


If you pull the support log from the AP, you can see some per-station debug info that lists the full table of rates (and even antenna patterns!) the AP likes to use to talk to your client. Remember that the higher MCS rates require both excellent SNR and minimal interference. Otherwise excessive retry rates may result in lower throughput compared to lower MCS rates.